How can I restrict the results from elasticsearch to only include parent-type documents? - elasticsearch

Question

I'm kinda stuck on this issue and struggling to find a solution:
I do have two types of entries in my shared Elasticsearch index, which are joined by a parent:child relationship.
I'd like to only receive documents of the "parent" type, but also include all "parent" documents which do not actually have child documents available.
Is there any way to implement this?
Best wishes,
Stefan

Answer 1

Below query is what you are looking for. I've made use of the Bool query
Let's say you have the below mapping for parent-child i.e. have question and its children are answer.
Mapping
PUT <your_index_name>
{
"mappings": {
"_doc": {
"properties": {
"my_join_field": {
"type": "join",
"relations": {
"question": "answer"
}
}
}
}
}
}
Query
POST <your_index_name>/_search
{
"query":{
"bool":{
"must":[
{ "term":{ "my_join_field":"question" }},
{
"bool":{
"must_not":[
{ "has_child":{
"type":"answer",
"query":{ "match_all":{} }
}
}
]
}
}
]
}
}
}
The above query would display all the parent documents i.e. question which doesn't have any children i.e.manswer.
Note that if you convert must_not into must in the above query, it would return you all the parent documents i.e. question which has children i.e answer ;)
Now if you want only parent documents. i.e. all the parent documents, your query would simply be in the below format:
Query for all parent documents
POST <your_index_name>/_search
{
"query":{
"bool":{
"must":[
{
"term":{
"my_join_field":"question"
}
}
]
}
}
}
OR it can be as simple as below:
POST <your_index_name>/_search
{
"query": {
"term": {
"my_join_field": "question"
}
}
}
Basically I've implemented Term Queries.
Let me know if it helps!